Practically all vacuum cleaners today are designed for use with a disposable dust bag, usually made of porous paper. However, there are times when it is desirable to empty and reuse the dust bag, but it must still be usable in a cleaner designed for a disposable bag, which bag is constructed to prevent the escape of any dirt therefrom, not only while the bag is in the cleaner, but also when it is removed for disposal. Thus, in U.S. Pat. No. 2,070,674 of Feb. 16, 1937, there is shown a disposable bag including an apertured cardboard disc provided with a flap valve opening inwardly so as to permit the entrance of airborne dirt while preventing the escape of dirt when the bag is removed from the cleaner.